This invention relates in general to a fluid displacement device. More particularly, it relates to an improved scroll-type fluid displacement device with a "sliding surface thrust bearing" and a "two way suction oil-gas passages" to assure sufficient lubricant supply to the thrust bearing under oil-mist lubrication condition and an "oldham ring with one sided keys" to maximize the working area of the sliding surface thrust bearing for variable speed applications.
Scroll-type fluid displacement devices are well-known in the art. For example, U.S. Pat. No. 801,182 to Creux discloses a scroll device including two scroll members each having a circular end plate and a spiroidal or involute scroll element. These scroll elements have identical spiral geometry and are interfit at an angular and radial offset to create a plurality of line contacts between their spiral curved surfaces. Thus, the interfit scroll elements seal off and define at least one pair of fluid pockets. By orbiting one scroll element relative to the other, the line contacts are shifted along the spiral curved surfaces, thereby changing the volume of the fluid pockets. This volume increases or decreases depending upon the direction of the scroll elements' relative orbital motion, and thus, the device may be used to compress or expand fluids.
Referring to FIGS. 1a-1d, the general operation of conventional scroll compressor will now be described. FIGS. 1a-1d schematically illustrate the relative movement of interfitting spiral-shaped scroll elements, 1 and 2, to compress a fluid. The scroll elements, 1 and 2, are angularly and radially offset and interfit with one another. FIG. 1ashows that the outer terminal end of each scroll element is in contact with the other scroll element, i.e., suction has just been completed, and a symmetrical pair of fluid pockets A1 and A2 has just been formed.
Each of FIGS. 1b-1d shows the position of the scroll elements at a particular drive shaft crank angle which is advanced from the angle shown in the proceeding figure. As the crank angle advances, the fluid pockets, A1 and A2, shift angularly and radially towards the center of the interfitting scroll elements with the volume of each fluid pockets A1 and A2 being gradually reduced. Fluid pockets A1 and A2 merge together at the center portion A as the crank angle passes from the state shown in FIG. 1c to the state shown in FIG. 1d. The volume of the connected single pocket is further reduced by an additional drive shaft revolution. During the relative orbit motion of the scroll elements, outer spaces, i.e. the suction chambers, which are shown as open in FIG. 1b and 1d, change to form new sealed off fluid pockets in which the next volume of fluid to be compressed is enclosed (FIGS. 1c and 1a show these states).
In some applications, such as in automobile air conditioning compressors, the compressor rotates at a speed variable from 800-6000 rpm, which is a big challenge to the thrust bearing of the compressor. It is unreliable to lubricate the thrust bearing in an automobile air conditioning compressor by an oil pump which is used in residential air conditioning compressors. It is because the oil level in the oil sump of an automobile air conditioning compressor constantly changes depending on the posture of the automobile, up hill, down hill or horizontal. Therefore, an oil mist lubrication scheme has been widely used in existing technology of automobile air conditioning compressors. In this scheme the amount of oil supplied to bearings is limited. The sliding surface thrust bearing with sufficient lubrication is inexpensive and capable to provide quiet operation and stable support. It is successfully used in residential scroll air conditioning compressors, but is not used in the automobile scroll air conditioning compressors due to the above mentioned reason. In stead, in an automobile air conditioning compressor, thrust ball bearing is used. The ball thrust bearing, for example, used in the scroll air conditioning compressors made by Sanden Corporation, tolerates less lubrication. However, the ball thrust bearing is expensive. It makes loud noises at high speed and wears out quickly due to the high contact stresses at the contact points between the balls and the races.
The present invention provides an improved scroll-type fluid displacement device. By providing a mechanism of two way suction oil-gas passages, most oil in the oil mist is collected and then directed to the sliding surface thrust bearing to meed the lubrication requirement and at the same time the suction pressure losses is minimized. The sliding surface thrust bearing is capable to operate at rotation speeds variable in a wide range. An oldham ring with one sided keys allows to maximize the working surface of the thrust bearing.